1. Field of the Invention
The present invention relates generally to hydraulic torque wrenches, and more specifically to hydraulic torque wrenches wherein the hydraulic cylinder is stationary with respect to the wrench housing.
2. Description of the Prior Art
Various methods have been used to link the piston rod of a hydraulic cylinder to the lever arm of a torque wrench. One well known method has been to allow the hydraulic cylinder itself to pivot along the arc made by the lever arm. This method requires a larger head to accommodate the hydraulic cylinder as well as the wrench housing. Additionally, there is the hazard and inconvenience of having exposed moving parts.
Another design method is to fixedly attach the hydraulic cylinder to the wrench housing. The piston rod is then linked to the lever arm by a ball joint or by slotted drive plates. Examples of stationary cylinder torque wrenches can be seen in in U.S. Pat. No. 4,201,099, issue date May 6, 1980.
These prior art wrenches, while being more maneuverable are also more prone to wear. A ball and joint linkage allows the piston rod to travel outside the cylinder axis thereby causing side loading of the piston. In the other systems, the piston rod also experiences significant side loads thereby enhancing the possibility of piston and cylinder wall wear and decreasing efficiency.